Diagnostic test device

ABSTRACT

A diagnostic test device comprising means for sampling a liquid biological sample, means for reacting the sample with at least one reagent to provide one or more visible indicia and an optical detector for detecting the presence of said one or more indicia, the device further comprising a releasable tether which is released by contact with the liquid sample, thereby to cause the optical detector to detect the said one or more indicia.

FIELD OF THE INVENTION

The present invention relates to a diagnostic test device such as apregnancy test device or a device such as for detection of a diseasestate, from a liquid biological sample. It may, for example, findapplication as a point of care (POC) diagnostic tool or other testdevice or for over-the-counter (OTC) sale. In such contexts, it ispreferably a disposable device.

BACKGROUND OF THE INVENTION

It is now commonplace to provide a disposable diagnostic device for theanalysis of a single analyte or multiple analytes that originate from aliquid biological sample. Examples of such devices include pregnancytests and glucose meters for diabetics. In the case of a typicalpregnancy test, urine is applied to a wick or collection zone, uponwhich the sample interacts and mixes with an antibody, or antibodiesthat specifically recognise the analyte of interest. One of theaforementioned antibodies is always coupled to a colourmetric indicator(often a gold sol or latex particle) for the visual interpretation of aresult and often considered as the primary antibody.

The sample and the released components pass through the associatedmaterials (often nitrocellulose) in a lateral flow manner. Deposited onto the nitrocellulose are two zones (or lines) of capture molecules. Thefirst zone (or line) is often the second antibody of a pair that detectsthe presence of the analyte of interest, however in some embodimentsthis line is composed of avidin or streptavidin that binds to a biotincoupled to antibody. The second line is often deemed as a control line,and comprises an antibody that specifically recognises the primaryantibody or a component bound to the surface of the colourmetricindicator.

The intensity of the first line of the two mentioned above isproportional to the quantity of analyte of interest present in thebiological sample. This is deemed as the test line. The second line isused to confirm whether the test has operated correctly, by releasingthe reagents, and fluid migrating appropriately. Together the linesrepresent the manner through which data can be extracted from theimmobilised immunoassay that takes place within the device.

In purely visual (i.e. human eye dependent) test devices, a non-skilleduser can be confused when a positive result is weak, it could be missedby the user, and considered as a negative, or provide the user with anambiguous result leading to uncertainty. This may lead to inappropriateconclusions.

It would therefore be desirable to provide an automated, preferablyelectronic, detector system whereby the risk of inaccuracy can bereduced in terms of determining more reliably, whether there issufficient contrast (colour change) between a test or control line zoneand background and also, to ensure that the line intensities areread/interpreted at the appropriate time post sample application.

Furthermore, our unpublished co-pending application GB0603665.1discloses the detection of active protease enzyme using a modifiedlateral flow immunoassay.

U.S. Pat. No. 4,791,461 discloses a portable analysis device comprisinga housing and an optical system consisting of a light source and aphotodetector. One or more test elements are mounted on a support stripand are used to perform an assay on a sample. The support is then placedin the housing and is caused to move relative to the housing and theoptical system so that the photodetector produces a change in outputsignal indicative of the reaction of at least one of the test elementsin response to the presence of a predetermined analyte in the sample.

SUMMARY OF THE INVENTION

Thus, the present invention provides a diagnostic test device comprisingmeans for sampling a liquid biological sample, means for reacting thesample with at least one reagent to provide one or more visible indiciaand an optical detector for detecting the presence of said one or moreindicia, the device further comprising a releasable tether which isreleased by contact with the liquid sample, thereby to cause the opticaldetector to detect the said one or more indicia.

The releasable tether is preferably formed of a material whichdisintegrates when wet, eg a water-soluble or water-friable material.

Preferably, the complete device, including electronic circuitry, isformed integrally in a unitary device. Alternatively, it may be embodiedas a device which does not include the circuitry for processing thephotodetector output and that circuitry may then be housed in a separateunit into which the device is plugged to obtain a readout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial cross-section through part of a diagnostic testdevice according to the present invention;

FIG. 2 shows an axial cross-section through the rear part of the deviceshown in FIG. 1, but depicting the optical detector system; and

FIG. 3 shows a variant of the construction shown in FIG. 2, representingan alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In one preferred class of embodiments, the device according to thepresent invention preferably comprises a housing, preferably an elongatehousing. The housing is not necessarily substantially closed but may beopen at one or more positions thereon, for example at least to exposethe sampling means. The housing is preferably substantially elongate.Typically, the overall length of such an elongate device is from 10 cmto 20 cm, preferably from 14 cm to 18 cm. Preferably, it has a width offrom 1 cm to 3 cm, more preferably from 1.5 cm to 2 cm.

Detection of one or more indicia includes the situations where only thepresence or absence of an indicium is determined (although this includesthe situation where the intensity of a corresponding photodetectoroutput is compared with a threshold), as well as quantitative orsemi-quantitative determination of the intensity of an indicium.

In the preferred class of embodiments, it is also preferred to providecapillary flow means, a region of which constitutes all or part of thesampling means. Preferably also, the detection zone is provided byanother region of the capillary flow means, most preferably thedetection zone being spatially separated from the sampling means.

It is especially preferred that the capillary flow means issubstantially elongate, the sampling means comprising a sampling zone atone end thereof, the sampling zone being separated from the detectionzone by a reagent zone. In such embodiments a mobilised reagent may bepresent in the reagent zone such as a labelled antibody capable ofbinding to an analyte of interest. A region (eg formed as a line)capable of capturing reagent and/or analyte after their interaction maybe present in the detection zone. When a labelled antibody is present inthe reagent zone, the capture region in the detection zone may comprisea second antibody capable of binding to a different epitope of theanalyte.

Where any one or more of the sampling zone, reagent zone and detectionzone are zones of the capillary flow means, they may be formed of thesame, or a different material, provided that the material or material(s)is or are chosen such as to permit flow from the sample zone to thedetection zone, eg. by virtue of having progressively decreasing poresize or fibre size. Suitable such materials include nitrocellulose,polyvinylidene fluoride, blotting paper, glass fibre and compressed ornon-compressed synthetic fabric fibres such as viscose or polyester,entangled fibres such as any of the foregoing or nylon membrane.

In a preferred class of embodiments, the one or more indica are locatedin a predetermined detection region. In such embodiments the opticaldetector preferably comprises a light source and a photodetector. Thelight source and photodetector may be arranged for detecting lightreflected from the detection region. Alternatively, the source anddetector may be arranged to determine transmissivity through a substratewhich comprises the detection region.

The releasable tether is preferably arranged such that upon its release,relative movement occurs between the photodetector and/or the lightsource, and the detection region. Such movement may for example, belinear or rotational, for example a rotational movement of the lightsource and/or photodetector. Preferably at least part of thephotodetector moves relative to the detection region and mostpreferably, relative to any housing. However, the alternativearrangement whereby the detection region e.g. of a sample strip, movesrelative to the photodetector parts, for example as described in U.S.Pat. No. 4,791,461, is also possible.

The detector may comprise a light source and a photodetector arrangedfor detecting light reflected from the detection region. Alternatively,the source and detector may be arranged to determine transmissivitythrough the detection region.

A secondary movement detector may also be provided, e.g. also as a lightsource/photodetector arrangement to trigger, by means of a mark providedfor the specific purpose of generating an output just before or justafter detection of at least one of the indicia, is to be expected.

Also in a generally preferred arrangement, upon release, thephotodetector and/or light source may be moved relative to the detectionregion by stored energy release means, such as spring means, for examplea coil spring. Alternatively, the motive force, following release, maybe provided by a miniature servomotor or other electrically operateddevice.

The releasable tether may comprise a material which disintegrates whenwet, e.g. a water-soluble or water-friable material, such as a watersoluble polymer (eg polyvinyl alcohol), gelatin, collagen, pectin,cellulose or sugar paper or any water-soluble organic or inorganic solidsuch as a sugar or an ionic salt such as an alkali metal chloride,hydroxypropylcellulose or hydroxymethyl cellulose, any of theseoptionally being admixed with a solubilising agent such as polyol, eg.glycerol.

Another alternative is to provide a material which disintegrates whenwet, for example tissue paper, crepe paper, or cigarette paper orethylene-acrylic acid sodium ionomers or microfibrillated cellulose,such as described in U.S. Pat. No. 6,821,531.

In yet another arrangement, the releasable tether may comprise fusemeans which is arranged to burn-out or be melted by passage of anelectrical current which is initiated substantially immediately bydetection of moisture, or after a predetermined time period for exampletriggered by a conductivity sensor. An example of a ‘melting fuse’ is awax member which is melted due to being heated by passage of theelectrical current through a filament. When a conductivity sensor isemployed, optionally, a suitable electrolyte may be impregnated into anappropriate substrate to allow passage of sufficient current through theconductivity sensor when wet.

The part or parts of the optical detector which move over the detectionregion is or are preferably mounted on a carriage, eg a carriagearranged to travel by virtue of a transport arrangement. For example,the carriage may comprise a projection arranged to travel in a slot or aslider disposed to move along a rail. Preferably, the transportarrangement comprises viscous damping means such as a predeterminedamount of a viscous liquid disposed over the projection or slider. Theviscous damping means slows and makes more uniform, the movement of thecarriage so as to prevent unwanted effects such as vibration, which mayinterfere with the reading or abrupt termination of movement through theimpact with a static object which is also capable of interference.

The detection region may also be provided with a stop indicator such asa black region or line. This is preferably situated near the end of thetravel of the moving part(s) of the detector means. Its function is toprovide a definite indication that a scan has occurred in the event thatneither a visible measurement indication nor a visible controlindication is produced.

The output of the optical detector is preferably processed by suitablecircuitry to produce a display for providing a visible indication of theresult of the test. This result may be qualitative (eg. the presence orabsence of the analyte of choice) or it may be semi-quantitative (eg. anapproximate value of analyte concentration in the sample).

Preferably, the device further comprises means for producing anelectrical signal indicative of loading of the sample. Preferably also,the device includes electronic timer means for determining the timeelapsed between production of the electrical signal indicative ofloading of the sample and production of the photodetector pulsed output.Electronic means may be provided for determining whether the determinedtime is within a predetermined time range and thereby producing anoutput indicative of whether or not a diagnostic test is valid. In thiskind of system, preferably the means for producing an electrical signalindicative of sample loading comprises a conductivity sensor.

An optional feature of the device is to provide the device with awetness sensor which may form part of the releasable tether. However, awetness sensor, preferably of the conductivity kind, eg using printedelectrodes on any capillary flow means, may be used to activate thesignal processing circuit. An appropriate circuit may be configured tobe activated after a predetermined time delay from first sensing ofmoisture by the wetness detector. This helps to avoid generation of afalse positive resulting from detection of a moving sample front in acapillary flow arrangement. For this purpose, the wetness detector mayfor example be positioned in a sampling zone, a reagent zone or in adetection zone, in the latter case preferably in a position which thesample front reaches before it reaches the position of the one or moreindica.

The non-functional components of the device (e.g. other than opticaldetector, sampling means, any means for sample transfer, the detectionregion, and any circuitry or display) may be made from any one or moresuitable materials but are preferably made from a mouldable plasticsmaterial such as ABS (Acrylonitrile-butadiene-styrene), acetals orpolyoxymethylenes (POM, Delrins), acrylics, butyls or polyisobutylenes(polybutenes), ethylene copolymers [(poly)ethylene acrylate acid (EAA),(poly)ethylene methyl acrylate (EMAC), (poly)ethylene ethyl acrylate(EEA), (poly)ethylene vinyl acetate (EVA), (poly)ethylene butyl acrylate(EBAC), (poly)ethylene vinyl acetate (EVA or EVAC), (poly)ethylene vinylalcohol (EVAL or EVOH), (poly)ethylene propyleneterpolymer (EPM)],fluoropolymers such as polytetrafluoroethylenes (PTFE) or polyvinylidenefluorides (PVDF), ionomers, liquid crystal polymers (LCP), PEEK orketones (polyaryletherketones or polyetheretherketones), polyethylenes,polyamides (nylons), polycarbonates, thermoplastic polyesters orterphthalates (PET, PBT), polyethylenes, polyether block amides (PEBA),polyetherimides, polyimides, polyolefins, polyphenylene oxides (PPO),polyphenylene sulfides (PPS), polypropylenes (PP), polysulphones,polyphthalamides (Aramids), thermoplastic polyurethanes, polyvinylidenechloride (PVDC), styrene or polystyrene, styrene acrylonitrilecopolymers (SAN, ASA, AES), styrene butadiene rubber (SBR), styrenemaleic anhydride (SMA), vinyl or polyvinyl chlorides (PVC), polylactides(PLA) and ethylene-vinyl acetates. It is especially preferred if anyhousing, carriage and transport mechanisms are formed from a mouldableplastics material.

The optical detector is intended to produce an electrical outputindicative of the result of the test, derived from detection of said oneor more indica. As described further below, this may be processed bysuitable circuitry and may be used to indicate the test result on adisplay.

The releasable tether is positioned such that it can be wetted by thesample when the sample reaches a predetermined position. Thus, where thedevice comprises capillary flow means, the releasable tether ispreferably touching, or more preferably anchored to the capillary flowmeans. In any event, before release it must be attached so as to keepthe movable part(s) of the photodetector, eg. by attachment to acarriage therefor, fixed relative to the body of the device.

Although a particularly preferred embodiment described below is in theform of a pregnancy test device, the present invention may also berealised in the form other diagnostic or similar test devices. Theinvention can be applied in any format that utilises multiple lines,areas of high/low contrast. Any assay format that has a line intensitychange in relation to background, be it colour or fluorescence mayemploy the present invention, but it is optimal in context of animmunoassay, and lateral flow strip technology.

The present invention will now be explained in more detail by way of thefollowing description of a preferred embodiment and with reference tothe accompanying drawings.

FIG. 1 shows a first embodiment of a diagnostic test device 1 accordingto the present invention. It comprises an elongate structure 3 ofgenerally planar configuration with its elongate dimension being shownfrom left to right in the drawing and its width being into the plane ofthe paper.

The device 1 comprises a sample collection wick 5 having a first samplecollecting end 7 at one end of the wick 5. At the other end 9 of thewick, a lower surface 11 of the wick is in contact with an upper surface13 of a reagent containing absorbent member 15, impregnated with tworeagents shown in zone 17. This zone comprises, as visual reportermolecules or particles, gold sol particles conjugated to one of abinding pair of primary antibodies 18, and a second reagent containingthe second of the antibody binding pair conjugated with biotin 18 b. Atthe other end of the reagent containing absorbent member 15, its lowersurface 12 in a region 19 is in physical contact with an upper surface21 of one end 23 of an assay reaction area absorbent member 25.

The assay reaction area absorbent member 25 is impregnated with twolinear zones 33 and 35 which respectively contain two reagents toconstitute a test line 33 and a control line 35. The test line 33contains avidin or streptavidin which specifically binds to thesecondary antibody reagent 18 b, and the control line 35 contains ananti-species antibody capable of specifically binding the primaryantibody: gold conjugate 18 independently of sample antigen.

The device, the main components of which are shown in FIG. 1, alsocomprises a transmissive optical detector for detecting the presence orabsence of colouration in the measurement line zone 33 and the controlline zone 35, although this mechanism is not depicted in FIG. 1. Thepurpose is to detect establishment of a relevant coloured reactionproduct within a range of predetermined times after the time in which aliquid sample is applied to the distal end 7 of the sample wick 5.

FIG. 2 shows in more detail the end of the device in the proximity ofthe distal end of the assay reaction area 31. This detector comprises anLED 41 and a phototransistor 43 mounted respectively above and below theplane of the assay reaction area absorbent member 25, and supported on amoveable carriage 45 which is in turn supported by a feature in thelower casework of the device 47. The carriage 45 and PCB 44, includingthe LED 41 and phototransistor 43 are held under tension by a coilspring 49 and a soluble tether 51 extending between the carriage 45 atlocation not on diagram, and an anchor point on the lower casework 47 ofthe device, also not shown on diagram. The soluble tether holds theoptical arrangement 41 and 43 to the side of the assay reaction area tothe proximal end 46 of the absorbent member.

Upon contact with sample, the soluble tether breaks at the point where afeature 50 in the upper casework 52 contacts the soluble tether 51 anddistal end of absorbent member 56 releasing the energy retained withinthe pre-tensioned coil spring 49 and allowing the carriage 45 andassociated components 41, 43, and 44 to traverse the assay reaction areacoming to rest at the distal end of the absorbent member 56.

As it travels, the LED 41 passes over, and the phototransistor 43travels directly beneath, the assay reaction area 33 and 35 in theabsorbent member 25. The electronic output signal of the phototransistor43 is conveyed via PCB 44 to circuitry integral with the device (notshown) to determine the relative contrast (optical density) between thetwo reaction zones 33 and 35 and background colour of the absorbentmember 25. In this way, the presence or absence of either or both testlines in zones 33 and 35 is readily determined to produce an outputindicative of (or not) of a clinical state of interest, such aspregnancy, and also the success or failure of the diagnostic test as awhole.

An alternative device for obtaining a semi-quantitative protease assayis constructed in similar manner to the device of FIGS. 1 and 2, exceptthe numerals used to depict certain features represent differentfeatures in the protease assay device. In one embodiment an extrareagent of a purified protein, in this case human chorionicgonadotrophin (hCG) is provided in an external vessel to which theprotease sample is added and given sufficient time to react with thepurified protein. Following incubation the sample is added to the deviceand allowed to migrate along the test strip and into the absorbentmember where the protein or its digested fragments are captured by thetest line one 33.

If the sample contains no protease the hCG remains intact and signalgeneration is strong at test line one 33 or of a decreasing signalintensity with increasing concentrations of protease. In addition, thetest line two 35 intensity (control line in a pregnancy test) iscorrespondingly opposed to that of the test line one, thus providing asecond indication of protease activity (e.g. test line 1 strong, testline 2 weak in low protease sample, test line 1 weak and test line 2strong in high protease activity).

In a second embodiment the reagent containing absorbent member 15 maycontain an extra reagent of the purified protein, in this case humanchorionic gonadotrophin (hCG). Interposed between the lower surface 12of the reagent containing absorbent member 15, in a region 19 and theupper surface 21 of one end 23 of an assay reaction area of absorbentmember 25 can be a soluble film that temporarily retards the flow ofsample through the liquid path of the device. Importantly, the delayoccurs once the sample (containing the protease of interest) hasinteracted with the labelled components and released the visual reportermolecules. This pause in flow enables the proteolytic enzymes to act onthe protease-sensitive peptides without the need of an additionalincubation step or complicated mechanical intervention. When the solublefilm has dissolved the test runs according to description above.

The said soluble film can be composed of, but not limited to; PVA,pectin, cellulose, modified cellulose, gelatine etc.

In general, the number of lines (indicia) located within the assayreaction area absorbent member 25 may optionally be greater than 2. Forexample, two or more first lines may be provided, each having labelledcomponents with protease-sensitive linker peptides which are sensitiveto different proteases. In such embodiments where each of the firstlines has a different label, a plurality of second lines may be providedeach capable of binding only one of the different labels. In this way,the presence of multiple different proteases may be detected in thesample.

In an alternative embodiment of the semi-quantitative protease assaydevice, the structure shown in FIG. 2 may optionally be modified by theinclusion of a movement detector, although this is not absolutelynecessary. This variant is shown in FIG. 3. A second photodetector 57 isemployed to record the contrast between a line and background bar codearrangement 58 within the device housing. This arrangement utilises aspecific illuminating LED 59. Alternatively, the existing illuminationLED 41 may be adopted for that purpose. However, in this alternativeembodiment, the PCB 44 generates a signal which is indicative of therelative intensity of the first and second lines and thus the relativeactivity of the protease enzyme in the sample.

In the light of the described embodiment, modifications of thatembodiment, as well as other embodiments, all within the scope of thepresent invention as defined by the appended claims will now becomeapparent to persons skilled in the art.

1. A diagnostic test device comprising means for sampling a liquidbiological sample, means for reacting the sample with at least onereagent to provide one or more visible indicia and an optical detectorfor detecting the presence of said one or more indicia, the devicefurther comprising a releasable tether which is released by contact withthe liquid sample, thereby to cause the optical detector to detect thesaid one or more indicia.
 2. A device according to claim 1, wherein theoptical detector comprises a light source and a photodetector, the saidone or more indicia being located in a predetermined detection region.3. A device according to claim 2, wherein the optical detector comprisesa light source and a photodetector arranged for detecting lightreflected from the detection region.
 4. A device according to claim 2,wherein the optical detector comprises a light source and aphotodetector arranged for detecting light transmitted through thedetection region.
 5. A device according to claim 2, wherein thereleasable tether is arranged such that upon its release, relativemovement occurs between the photodetector and/or the light source andthe detection region.
 6. A device according to claim 5, wherein therelative movement is completed within a time period of from 0.1 to 2seconds.
 7. A device according to claim 5, wherein said relativemovement is linear movement.
 8. A device according to claim 5, whereinsaid relative movement is rotary.
 9. A device according to claim 5,further comprising damping means for damping said movement.
 10. A deviceaccording to claim 8, wherein said rotary relative movement isrotational movement of the light source and/or photodetector.
 11. Adevice according to claim 5, wherein upon release, the photodetectorand/or light source is or are moved relative to the detection region byspring means.
 12. A device according to claim 5, wherein upon release,the photodetector and/or light source is or are arranged to be moved byone or more of gravity, inertia, gas release and electromotive means.13. A device according to claim 5, wherein the releasable tethercomprises a water-soluble material.
 14. A device according to claim 13,wherein the water-soluble material is selected from a water-solublepolymer such as polyvinyl alcohol, collagen, gelatin, pectin or sugarpaper or any water-soluble organic or inorganic sold such as a sugar oran ionic salt such as an alkali metal chloride, hydroxymethyl celluloseor hydroxypropyl cellulose, any of said materials optionally being inadmixture with a solubilising agent such as a polyol, eg glycerol.
 15. Adevice according to claim 5, wherein the releasable tether comprises amaterial which disintegrates when wet.
 16. A device according to claim15, wherein the material which disintegrates when wet is selected fromtissue paper, crepe paper, or cigarette paper or ethylene-acrylic acidsodium ionomers or microfibrillated cellulose.
 17. A device according toclaim 5, wherein the releasable tether comprises fuse means which isburned-out or melted by virtue of passage of an electrical current whichis initiated by detection of moisture.
 18. A device according to claim17, further comprising a conductivity sensor for detection of themoisture.